It is well known that Diesel internal combustion engines and particularly Diesel truck engines obtain optimum performance and efficiency when using #2 Diesel fuel. However, in cold weather conditions, such fuel becomes extremely viscous and as temperatures fall into sub-zero ranges, the #2 fuel can actually become too thick to pass through fuel filters. Even if the fuel is able to flow through the filter to the engine, it may be too cold to ignite. And even if ignition does result, performance and efficiency suffer.
Previous attempts were made to solve the problem by blending the #2 Diesel fuel with the less viscous #1 Diesel fuel. The mixture of fuels aided cold weather ignition, but power was reduced, performance suffered, engine life was shortened because the advantageous lubrication qualities of pure #2 fuel were lost, gas mileage dwindled because of the lower B.T.U. content of #1 fuel, and it was still impossible to maintain the engine idle speed at very low outside temperatures.
A successful solution to some of the cold weather Diesel engine starting problems exhibited with pure #2 fuel or with The #1 and #2 fuel mixture was enunciated in U.S. Pat. No. 3,929,187. Therein a heat exchanger was mounted on an internal combustion engine for preheating low temperature, highly viscous fuels prior to burning in the engine. Such exchangers reduced the viscosity of the fuel, eliminated fuel filter clogging, allowed the use of pure #2 Diesel fuel, and improved fuel burning efficiency.
Heat exchangers for preheating fuel and particularly Diesel fuel are now commonly employed in commercial Diesel truck engines. Some of these heat exchangers are warmed by exhaust pipe gases, but the far more prevalent and efficient systems transfer heat in the exchangers to warm fuel passing therethrough by using the engine-coolant fluid from the radiator and engine block. As the engine ignites and continues to run, temperatures in the engine compartment warm the coolant which, in turn, is used to preheat the fuel. However, there exists a point wherein the coolant from the very hot engine warms the fuel to a temperature in excess of a critical value. That value is determined as the temperature at which the heated fuel will scorch parts of the fuel injection assembly and normally occurs at approximately 180.degree. F.
It is therefore one object of the present invention to provide a system for controlling the temperature of fuel flowing into an internal combustion engine by sensing the temperature of the fuel approximate the outlet port of the heat exchanger and preventing the inflow of hot coolant when the temperature rises above the predetermined critical value.
While previous heat exchangers helped to maintain the operational efficiency of Diesel engines burning #2 Diesel fuel, despite frigid outside temperature conditions, they did not aid the initial ignition of the fuel in the cold engine. When the engine is started in zero degree temperatures, after a prolonged period of non-use, the coolant is just as cold as the fuel. Consequently, the coolant cannot effectively transfer heat to the fuel flowing through the heat exchanger.
It is yet a further object of the present invention to provide a heat exchanger for warming internal combustion engine fuels at times that the engine, fuel and coolant are as cold as the outdoor temperature, the exchanger including an additional heating element connected to an external power supply.
These and other objects and advantages of the invention will become clear from the following description of a preferred embodiment of the invention.